In completely or partially combustion heated high-temperature furnaces such as a glass melting furnace, pollution is a frequently encountered problem. High emission levels of pollutants such as oxides of nitrogen (NO.sub.x), sulfur dioxide (SO.sub.2), carbon dioxide, and particulates, which often exceed the maximum levels permitted by the Environmental Protection Agency Regulations are typical for furnaces with air-fuel fired and oxygen enriched air-fuel fired burners.
In the past, the problem has been addressed by using post-combustion pollutant reduction techniques. However, these processes require equipment that makes the solution extremely capital intensive and costly to operate. Another and more efficient method is using oxygen in the combustion process to eliminate nitrogen from the air and reduce the NO.sub.x and particulate emissions to below the guidelines suggested by the Environmental Protection Agency. In addition, the use of oxygen in combustion reduces carbon dioxide emission through an increase in heating efficiency of the furnace and brings numerous other benefits ranging from increased production capacity to savings in batch chemicals.
Oxygen-fuel burners may be divided into two major groups, those that are water cooled and those that are gas cooled. A frequently encountered problem with the burners of either group is the lack of a diluent and carrier gas; e.g., nitrogen, which increases partial pressures of volatile batch components and accelerates corrosion rates of metallic and ceramic materials used for burner construction. Thus, build-up and corrosion on water or gas cooled burner nozzles are the most common problems in high temperature furnaces. A large temperature difference between the cooled burner nozzles and furnace gases causes condensation of volatile and corrosive species and build-up on the burner nozzle. This is reported in an article entitled "Oxygen Firing at Parkersburg" by D. Shamp and D. Davis in the December 1990 edition of American Glass Review. In a gas cooled or water cooled burner where the water cooling is not at optimum flow rates, build-up on the nozzles can cause flame deflection and impingement on the burner nozzle leading to damage or destruction of the burner.
A second problem encountered with water and gas cooled oxy-fuel burners is the fact that the refractory burner block, often used to enable installation of the burner into a furnace and/or to increase flame stability, involves an opening with an inner diameter much larger than the flame jet diameter causing entrainment of corrosive furnace gases or particulate material inside the block and contact with the burner. This type of burner is shown in U.S. Pat. No. 4,690,635.
Another problem, to both the water and gas cooled burners is low flame luminosity because of a high burning velocity and rapid mixing rates encountered in such combustion systems. This decreases the heating efficiency since radiation is the major heat transfer mechanism in a high temperature furnace such as a glass melting furnace.
In addition, water cooled oxy-fuel burners require capital investment and maintenance. Such burners may lower the overall heating efficiency of a furnace by extracting considerable heat from it with the flow of cooling water. For example, for a burner cooling water flow rate of 5 gallons per minute, and output to input water temperature difference of 50.degree. F., heat loss per burner is approximately 125,000 Btu's per hour. For a 10-burner furnace the heat loss due to the water-cooling amounts to about $30,000 per year. In addition, there is always the possibility of water leakage into the furnace if a burner is not maintained properly and there is a risk of clogging and corrosion of the burner water cooling channels if poor water quality is the only means of cooling available to the user.
Gas-cooled oxy-fuel burners can present a problem in the case of interruption in the fuel or oxygen supply. Such burners have to be immediately removed from the firing port in the furnace to prevent possible damage from the high temperature present in the furnace. If such burners rely upon metal fins at the burner face to cool the burner, these fins can collect condensation and result in corrosion problems with the burner.